<?php
/*
 * Copyright 2015 Google Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

namespace Google\Auth;

use Google\Auth\Credentials\ServiceAccountCredentials;
use Google\Auth\Credentials\UserRefreshCredentials;

/**
 * CredentialsLoader contains the behaviour used to locate and find default
 * credentials files on the file system.
 */
abstract class CredentialsLoader implements FetchAuthTokenInterface
{
    const TOKEN_CREDENTIAL_URI = 'https://www.googleapis.com/oauth2/v4/token';
    const ENV_VAR = 'GOOGLE_APPLICATION_CREDENTIALS';
    const WELL_KNOWN_PATH = 'gcloud/application_default_credentials.json';
    const NON_WINDOWS_WELL_KNOWN_PATH_BASE = '.config';
    const AUTH_METADATA_KEY = 'Authorization';

    /**
     * @param string $cause
     * @return string
     */
    private static function unableToReadEnv($cause)
    {
        $msg = 'Unable to read the credential file specified by ';
        $msg .= ' GOOGLE_APPLICATION_CREDENTIALS: ';
        $msg .= $cause;

        return $msg;
    }

    /**
     * @return bool
     */
    private static function isOnWindows()
    {
        return strtoupper(substr(PHP_OS, 0, 3)) === 'WIN';
    }

    /**
     * Load a JSON key from the path specified in the environment.
     *
     * Load a JSON key from the path specified in the environment
     * variable GOOGLE_APPLICATION_CREDENTIALS. Return null if
     * GOOGLE_APPLICATION_CREDENTIALS is not specified.
     *
     * @return array JSON key | null
     */
    public static function fromEnv()
    {
        $path = getenv(self::ENV_VAR);
        if (empty($path)) {
            return;
        }
        if (!file_exists($path)) {
            $cause = 'file ' . $path . ' does not exist';
            throw new \DomainException(self::unableToReadEnv($cause));
        }
        $jsonKey = file_get_contents($path);
        return json_decode($jsonKey, true);
    }

    /**
     * Load a JSON key from a well known path.
     *
     * The well known path is OS dependent:
     * - windows: %APPDATA%/gcloud/application_default_credentials.json
     * - others: $HOME/.config/gcloud/application_default_credentials.json
     *
     * If the file does not exists, this returns null.
     *
     * @return array JSON key | null
     */
    public static function fromWellKnownFile()
    {
        $rootEnv = self::isOnWindows() ? 'APPDATA' : 'HOME';
        $path = [getenv($rootEnv)];
        if (!self::isOnWindows()) {
            $path[] = self::NON_WINDOWS_WELL_KNOWN_PATH_BASE;
        }
        $path[] = self::WELL_KNOWN_PATH;
        $path = implode(DIRECTORY_SEPARATOR, $path);
        if (!file_exists($path)) {
            return;
        }
        $jsonKey = file_get_contents($path);
        return json_decode($jsonKey, true);
    }

    /**
     * Create a new Credentials instance.
     *
     * @param string|array scope the scope of the access request, expressed
     *   either as an Array or as a space-delimited String.
     * @param array $jsonKey the JSON credentials.
     *
     * @return ServiceAccountCredentials|UserRefreshCredentials
     */
    public static function makeCredentials($scope, array $jsonKey)
    {
        if (!array_key_exists('type', $jsonKey)) {
            throw new \InvalidArgumentException('json key is missing the type field');
        }

        if ($jsonKey['type'] == 'service_account') {
            return new ServiceAccountCredentials($scope, $jsonKey);
        } elseif ($jsonKey['type'] == 'authorized_user') {
            return new UserRefreshCredentials($scope, $jsonKey);
        } else {
            throw new \InvalidArgumentException('invalid value in the type field');
        }
    }

    /**
     * export a callback function which updates runtime metadata.
     *
     * @return array updateMetadata function
     */
    public function getUpdateMetadataFunc()
    {
        return array($this, 'updateMetadata');
    }

    /**
     * Updates metadata with the authorization token.
     *
     * @param array $metadata metadata hashmap
     * @param string $authUri optional auth uri
     * @param callable $httpHandler callback which delivers psr7 request
     *
     * @return array updated metadata hashmap
     */
    public function updateMetadata(
        $metadata,
        $authUri = null,
        callable $httpHandler = null
    ) {
        $result = $this->fetchAuthToken($httpHandler);
        if (!isset($result['access_token'])) {
            return $metadata;
        }
        $metadata_copy = $metadata;
        $metadata_copy[self::AUTH_METADATA_KEY] = array('Bearer ' . $result['access_token']);

        return $metadata_copy;
    }
}
